1. Field of the Invention
The present invention relates to an image formation apparatus in a copying machine, facsimile, printer, or the like.
2. Description of the Related Art
In a wet toner process, a liquid developer containing charged toner particles in a carrier liquid is used for forming a developed image with toner on a developing image carrier on which a latent image has been formed, and the developed image is fixed onto a recording medium such as paper. In such a wet toner process, a photosensitive body serves as a carrier of the latent image and the developed image.
Moreover, when using a liquid developer, transfer and fixation onto a recording medium requires squeezing and drying for removing the carrier liquid in the developed image.
Moreover, in the method using a liquid developer, a developed image is formed directly on a photosensitive body, the photosensitive body should have predetermined characteristics (swelling property, heat resistance, and a long service life), which increases production costs.
During development, a developing roller is used to supply a liquid developer onto a latent image carrier (photosensitive body). The liquid developer always is in contact with the latent image carrier. The liquid developer is also applied to a non-image portion, thus the carrier liquid is wasted, a surplus liquid developer (especially, carrier liquid) is wasted before and after an image formation, squeezing and drying are required, a change of the liquid developer characteristics due to contact with the latent image carrier occurs, the image formation is not stable, and the running cost is increased.
Furthermore, since a belt-shaped photosensitive body is often used, troublesome replacement of the belt-shaped photosensitive body is required, which also costs much, thus increasing the running cost.
Moreover, in order to obtain a high-speed and high-quality color image by the electro-photograhic method, it is possible to employ a tandem type image formation apparatus using a liquid developer which can use a small-diameter toner and a plurality of exposure systems and developing units. However, when using a single photosensitive body, charging, exposure, and developing units arranged around the photosensitive body, having different mounting angles with respect to the drum shape, and the developing unit using a liquid developer requires a solvent removal step. This complicates the design configuration, and the size of the photosensitive drum diameter is increased.
Moreover, in a case of superimposing color images on the photosensitive body using a liquid developer, a carrier liquid of the liquid developer is in direct contact with the photosensitive body. Accordingly, the photosensitive body should have countermeasures against swelling and squeezing and drying durability, which costs much. Moreover, when color superimposing is performed on the photosensitive body, a toner layer developed first reduces the exposure amount for the next color development exposure, impinging accurate color reproduction.
When a plurality of photosensitive drums are used, if development is performed on the photosensitive body surface, the photosensitive drums should have countermeasures against swelling and squeezing and drying durability.
Furthermore, when development is of a contact type using a developing roller, the liquid developer is applied also to a non-image portion, and a carrier liquid is applied to the image portion. Later, the carrier liquid should be removed. This increases the load on the image carrier. When using an intermediate transfer body, if development is performed on the photosensitive body, the photosensitive body should have special characteristics and the apparatus size should be fairly large.
On the other hand, there has been suggested a process to transfer a latent image from a photosensitive body to a film and then develop the latent image. That is, a film is brought into contact to the photosensitive body on which a latent image has been formed, and then the image is developed with powder. This latent image transfer does not occur sufficiently, and the powder development cannot realize a high resolution.
Furthermore, there is a method for exposing the photosensitive body having a fixed film. In this case, the film should be transparent. However, the film is often stained by the developer, decreasing the reliability.
Moreover, in a conventional color image formation apparatus using an intermediate transfer film, a photosensitive body on which an electrostatic latent image is formed, is covered with film and powder developer. Sufficient electrostatic transfer cannot be obtained only by covering with the photosensitive body film and powder, thus development cannot realize a high-resolution image. Furthermore, there is a method to expose the photosensitive body covered with an intermediate transfer film. In this case, the film should be transparent. The developer may stain an unnecessary portion, decreasing the reliability.
Japanese Patent Publication No. 6-236092 discloses a method in which an electrostatic latent image formed on a photosensitive body is electrostatically transferred onto an intermediate transfer film and a liquid developer is used, but a single exposure system is used. Moreover, since developer is performed by a roller development, i.e., a contact type, a non-image portion is stained, carrier liquid is consumed, and excessive amount of liquid developer (especially carrier) is consumed before and after the image formation. All of the above increase load on the squeezing and drying process, lowering durability. Furthermore, respective color developing units are arranged at a portion where the belt-shaped photosensitive body and the intermediate transfer film are superimposed, which makes the photosensitive body large.